fix: sync Quick Prompt popup theme with main app

The popup window has its own document and never received the
data-theme attribute. Pass the current theme setting from the main
process via the show event, resolve 'system' to effective dark/light,
and apply to document.documentElement.dataset.theme so all CSS
variables match the main app's appearance.

- Add getCurrentTheme() to AryxAppService
- Pass theme in toggleQuickPromptWindow / showQuickPromptWindow
- Update onShow listener signature to receive theme string
- Apply theme to documentElement on each popup activation

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/preload/quickprompt.ts

@@ -36,7 +36,7 @@ const api: QuickPromptElectronApi = {
     return () => ipcRenderer.off(ch.sessionEvent, handler);
   },
   onShow: (listener) => {
-    const handler = () => listener();
+    const handler = (_event: Electron.IpcRendererEvent, theme: string) => listener(theme);
     ipcRenderer.on(ch.show, handler);
     return () => ipcRenderer.off(ch.show, handler);
   },